RESPIRATION 8l 



But such intracellular differentiation' has limits, because 

 a cell is unworkable if it exceeds a certain size, and the 

 elaborate differentiation of the higher organisrhs depends 

 upon their multicellular structure. 



(5) Respiration. — The functions hitherto considered 

 are all concerned with building up the protoplasm of 

 the organism. We have now to consider processes con- 

 nected with the expenditure of energy by the organism 

 and with the breaking down of organic substances. 



When the amoeba moves it does work and spends 

 energy in doing it. This energy is derived from the 

 energy locked up (potential energy) in the molecules of 

 organic substance taken in as food — largely in( the 

 carbohydrates. The molecules of these substances are 

 broken down into simpler substances and largely 

 oxidised in the process, the energy being set free and 

 appearing in the kinetic form, i.e. as mass motion — 

 for instance, the streaming of the amoeba cytoplasm — 

 and heat. Free oxygen is necessary to carry out this 

 process, and that is why free oxygen is required by 

 very nearly all living beings. Aquatic organisms get 

 their oxygen from that which is dissolved in the water 

 they hve in, terrestrial forms direct from the air. In 

 its absence the activity of the organism comes to an end. 



The release of energy is obtained almost entirely by 

 the oxidation of sugar (glucose) with the formation of 

 carbon dioxide and water. 



The generalised equation is : — 



CeHiaOe + 60^ = 600^ + 6H2O 

 glucose oxygen carbon water 

 dioxide 

 potential energy — > kinetic energy 



(mass motion and heat) 



This process is what is called in biology respiration. 

 " Difierentiation within the cell, from Latin intra, within. 



6 



